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Arc-Weldable Strain Gauge

  • Arc-Weldable Strain Gauge

Designed to measure strain in steel, this vibrating wire strain gauge is held to the structure by mounting blocks are arc-welded to the structure. Groutable mounting blocks are available for concrete structures. Readings are obtained with a VW readout or data logger.

Typical applications include:

  • Monitoring structural members of buildings and bridges during and after construction.
  • Monitoring load in struts used to brace deep excavations.
  • Measuring strain in tunnel linings and supports.
  • Monitoring areas of concentrated stress in pipes.
  • Monitoring distribution of load in pile tests.
  • Monitoring cracks in concrete (may require long-base strain gauge).

Advantages of the Arc-Weldable Strain Gauge include:

  • Field Adjustable – The strain gauge can be adjusted so that most of its range is available to measure compression or tension, as required by the application.
  • Removeable Coils – The coils used to excite and read the vibrating wire can be removed from the strain gauge to be used on future installations.
  • Built-in Temperature Sensor – The temperature sensor is useful for temperature corrections when the gauge is installed on materials that have a different temperature coefficient.
  • Easy Installation – The mounting system ensures that the gauge is not damaged during installation of the mounting plates. Also, this mounting system allows repositioning or reuse of the gauge.
  • Reliable Signal Transmission – The strain gauge provides a strong signal which can be transmitted reliably over long distances with properly shielded cable.
  • Limitations – Requires spot-welder, not suitable for high-speed dynamic measurements.

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Arc-Weldable Strain Gauge Specifications

ARC-WELDABLE STRAIN GAUGE
Strain Gauge52641360Strain gauge with a thermistor. Anchors, clip-on pickup, and signal cable are ordered separately
Range3,000 microstrain. User can set tension to maximize range for the application
Resolution1 microstrain with VW Indicator
Accuracy± 0.5% FS
Thermal Coefficient11ppm / °C
Length150 mm (5.875″)
Operating Temperature-20°C to +80°C
Temperature Accuracy±0.5°C (at 0°C to 70°C)
ANCHORS
Weldable Anchors52641320Two mounting-blocks with set-screws. Used if welding strain gauge to steel structures
Groutable Anchors52641325Two mounting blocks with 3″ long groutable anchors attached. Used to mount strain gauge to concrete
INSTALLATION ACCESSORIES
Installation Kit52641330Kit includes one spacer rod, an Allen wrench, and two spare set screws.
PICKUP AND SIGNAL CABLE
VW Standard Clip-on Pickup52641110Standard clip-on pickup includes 10 feet (3 m) of signal cable and a hose clamp
VW Custom Length Clip-on Pickup52641100Custom clip-on pickup includes the pickup and a hose clamp. Signal cable must be ordered separately and will be installed at the factory
Signal Cable50613824Shielded cable with four 22-gauge tinned-copper conductors and flexible polyvinyl chloride (PVC) jacket
Terminal Box for 6 sensors57711606Provides terminals for signal cable from 6, 12, or 24 sensors. Sensors are selected by rotary switch. Dimensions of 6-sensor box are 240 x 190 x 120 mm (9.5 x 7.5 x 4.75″). Dimensions of 12 and 24-sensor boxes are 290 x 345 x 135 mm (11.5 x 13.5 x 5.25″)
Terminal Box for 12 Sensors57711600
Terminal Box for 24 Sensors97711624
Universal Connector57705001For terminating a single cable. Connector not required when sensors are connected to a terminal box, a data logger, or to the terminal posts on the VW Data Recorder
READOUT
VW Data Recorder52613500The VW Data Recorder displays VW sensor readings in Hz or Hz2 /1000 and thermistor data in degrees C. It can also record the readings. See separate datasheet
Jumper Cable for Terminal Box52613557The jumper cable is required when the VW Data Recorder is to be connected to a terminal box or to a connector attached to signal cable
DATA LOGGERS
VW MiniLogger52613310The VW MiniLogger is a compact, low-cost data logger for one sensor. See separate datasheet
4-Channel V-Logger52615140
8-Channel V-Logger52615180
Campbell Scientific Data LoggersCampbell data loggers with a VW interface and the AM16/32 multiplexer can accommodate 16 sensors with temperature readings or 32 sensors without temperature readings

The strain gauge operates on the principle that a tensioned wire, when plucked, vibrates at its natural harmonic frequency, and by measuring that frequency, we can calculate the strain in the wire. The gauge is constructed so that a wire is held in tension between two mounting blocks that are welded to the structural member. Loading of the structural member changes the distance between the two mounting blocks and results in a change in the tension of the wire. An electromagnet is used to pluck the wire and measure the frequency of vibration. Strain is then calculated by applying calibration factors to the frequency measurement.

The strain gauge is supplied with two mounting blocks which are arc-welded to the steel surface. For applications on concrete, small holes are drilled into the structure and groutable mounting blocks are used.

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